In the spring of 1846, William and Elizabeth Darmon receive a mysterious letter from a soldier dying on a Punjab battlefield. Soon after, a Sikh refugee arrives at London dock pursued by a Russian agent who kills the warrior and kidnaps Elizabeth. William trails them to India and confronts the predator high on Rakaposhi Mountain. Then the unthinkable happens: Cossacks invade over the Himalayas to join a rebel leader in Jammu. Within the war-torn province, the Darmons make their way back and find a letter from Tsar Nicholas alluding to a Russo-American agreement to eliminate British presence in North America by the sale of Northwest territories. Using the proceeds, the Emperor plans an invasion of the Crimea. The Darmons race across the Taklamakan desert, Afghanistan, and Persia under pursuit of Cossacks and Khiva warriors in an attempt to warn Abd al-Majid, Sultan of the Ottoman Empire.